Reactive power control can be used to optimize reactive power flow within an electric power network, denoted power network in the following. A Static VAR (Volt-Ampere Reactive) Compensator (SVC) is a device frequently used within such power networks for combating disturbances within the network by means of reactive power. The SVC counteracts voltage drops in the power network by providing reactive power and is often able to handle overvoltages by absorbing reactive power. In short, the SVC works to maintain the voltage of the power system by adjusting the reactive power flow, as the reactive power is a great factor of voltage fluctuations in the power network.
To this end, the typical SVC comprises a bank of thyristor-switched capacitors, harmonic filters and thyristor-controlled inductive elements, also denoted reactors. These components of the SVC are controlled so as to provide the desired reactive power. In particular, if the power network's reactive demand is capacitive (leading) the SVC uses the reactors to consume VARs from the network, thereby lowering the system voltage. If the power network's reactive demand is inductive (lagging) the capacitor banks are used for supplying VARs to the power network, thereby increasing the power network voltage.
The SVC comprises a control system for controlling the above-described functions. The control system is most often of a PI (proportional-integral) type, or just of I-regulator type. A voltage in the power network is measured at some point by means of a suitable voltage-detecting device. The measured voltage is compared to a set reference voltage, and the control system outputs a reactive power control signal commanding the SVC to provide or absorb reactive power in dependence on the power network need, which, somewhat simplified, is determined in dependence on the difference between the measured voltage and the set reference voltage.